Cool experiment. But I don't recommend getting into Ethereum mining now, as the network is on the verge of switching to Proof of Stake as part of the migration to Ethereum 2.0.
I made ~$100 in the past month (stopped during the cold snap/storm here) on my 3080 mining ETH. Of course, I was getting closer to 90Mh/s so slightly more viable.
But I personally wouldn't make a big investment on it if I was only getting started now.
Maybe (hopefully) we'll see environmental regulations against (expensive PoW) cryptocurrency before theres economically motivated regulation.
I found this analysis insightful: https://coinshares.com/insights/beware-of-lazy-research-bitc...
Also this Twitter thread (12 tweets) and all the articles linked inside it: https://twitter.com/yassineARK/status/1360343401627979778
Nodes will still verify transactions and execute smart contracts, of course. But there's no hash lottery to be won for mining blocks.
At this point, most crypto projects with any real traction (with the obvious exception of Bitcoin) are either ERC-20 tokens running on Ethereum, or other PoS chains that claim to be better than Ethereum (i.e. Cardano).
Bitcoin isn't mined with GPUs anymore.
Sure, some of it will move to other currencies, but my guess would be it won't be anywhere near 100% as you're suggesting.
Secondly, I tend to think there'll be a mass extinction event, where most useless projects will eventually die off. You can mine all you want, but if there's no real utility in yet another PoW project (and there isn't), you won't be able to sell the coins at a price that justifies running the operation.